It makes me wonder: where does thermal expansion in solids come from, anyway? There seems to be a parallel with the ideal gas law, but because the nuclei are far more constrained, the bonds must be stretchy, and since the material has to have some way of storing heat in the steady state, the only place I can think of is vibration of the bond. But how does a vibrating bond lead to expansion? In theory a strong enough bond could store infinite energy, as the modes get higher.